A silicone resin is known in the related art as a resin having heat resistance which hardly shows change in hardness in an atmosphere of 100 to 150° C. Main skeleton of a silicone resin has a spiral shape, and heat resistance is exhibited by such unique skeleton. However, as containing low molecular weight siloxane (i.e., cyclic siloxane of D3 to D10), the silicone resin may have an adverse influence on an electrical and electronic part. Further, a silicone resin of moisture curing type requires a certain period of time for deep section curing. A silicone resin of heat curing type also requires a heating period. For such reasons, it is disadvantages in terms of workability compared to a photocurable type resin which is cured by irradiation with energy rays like UV rays.
A (meth)acryl polymer having a (meth)acryl group at both terminals (hereinafter, also referred to as a “polymer (A)”) is a known material, and a cured product of the polymer (A) is known to have elasticity and is used as a material for substituting a silicone resin. Although the polymer (A) has advantages that it can be cured by light and/or heat and also does not generate a low molecular weight siloxane, it is difficult to form a cured product with soft property peculiar to a silicone resin. In recent years, a (meth)acryl polymer having a (meth)acryl group at only one terminal (hereinafter, also referred to as a “polymer (B)”) is known and, by mixing the polymer (A) with the polymer (B), a possibility of obtaining the same elasticity as the silicone resin has been found. However, by simple mixing as described in Patent Literature 1, a sticker is obtained but it is not suitable for applications as a sealing agent and an adhesive.
It has been also reported to use an active energy curable type composition obtained by mixing the polymer (A) and the polymer (B) as a form-in-place gasket as described in Patent Literature 2, in which a sheet-like cured product is produced first by irradiation with light and the permanent compression set is measured. The composition for a form-in-place gasket indicates that the composition is applied in place and cured by irradiation with energy rays in the same place to form a gasket. Thus, investigation on the composition needs to be made in terms of properties including viscosity and fluidity. In general, when an organic filler and/or an inorganic filler for controlling viscosity are not added, dripping of the composition occurs as the properties are not maintained, and thus it cannot be used as a gasket. On the other hand, in accordance with addition of a filler, physical properties of the cured product change. Further, when a sealing material is produced by punching after curing into a sheet-like form, remaining sheets are yielded, and thus poor production efficiency is caused. For such reasons, forming a sealing material by in-place applying enhances production efficiency.